1. Field of the Invention
This invention relates generally to aircraft lighting systems, and more particularly to an improved LED current regulation circuit for providing continuous electrical current to LEDs in aircraft lighting systems, in particular, aircraft emergency evacuation systems, through a varying voltage source.
2. Description of the Prior Art
During the course of a nighttime aircraft emergency scenario, it is critical that proper egress pathways are illuminated to allow passengers to safely exit the aircraft. Needless to say, a failure of one or more light sources may prove disastrous.
To understand the impact of a failed aircraft lighting system, one need only imagine a scenario at sea, where passengers of a downed aircraft must exit the aircraft by exiting the aircraft into a slide raft. With out proper lighting to illuminate the landing zone, passengers may find themselves fighting for their lives in the ocean instead of remaining safely in the slide raft.
One means of providing sufficient lighting in an aircraft emergency situation is via the use of Light Emitting Diodes (LEDs). LEDs produce a bright beam of light at a lower power consumption than most incandescent light bulbs. The problem with traditional incandescent lights is that they are very inefficient at producing light as most of the energy required to produce the light is wasted as heat. LED lights give off less heat in the generation of light and require much less current. In a dark environment, LEDs are usually bright enough to cast shadows more than 10 feet away.
Further, regular incandescent light bulbs generally last for six to eight thousand hours (about 1 year) before burning out. The white LEDs have a bulb life rated at 100,000 hours or 11 years. Also, LED lights are very efficient at producing light using 90% less energy than incandescents. These two advantages combined with the fact that LEDs can withstand greater shock and vibration, and possess greater tolerance to heat, cold, and moisture far beyond those tolerated by incandescent lamps, make the LED a far superior source for light. The overall advantages of the LED lights make them ideal for aircraft emergency evacuation situation.
However, LEDs are not without inherent difficulties. It takes a number of LEDs in clusters to produce enough light to match the incandescent, and they are generally more expensive. Further, when the input voltage varies through a wide range of voltages, there exists a high probability that a low voltage will cause the LED to emit insufficient light, whereas too high a voltage will cause the LED to overheat and damage the unit.
It is often desirable to maintain the current through one or more LEDs through a wide raging fluctuation of input voltages. This is done through the use of a current regulator. Typical current regulators use resistors to limit the current to a set range based on input voltage. Resistors compensate for changes in the load of the input voltage. However, resistors often do not adequately respond to compensate for these changes, rendering circuits of this type ineffective.
Accordingly, what is needed in the art is a current regulator circuit used to provide a constant, reliable, low cost flow of electrical current to one or more LEDs in an aircraft illumination system, thereby providing optimum lighting despite wide input voltage fluctuations.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
In a preferred embodiment of the present invention, an apparatus for illuminating an aircraft lighting system is provided, which utilizes a unique current regulation circuit for providing a fixed current throughout one or more light sources.
Generally, the apparatus is an illumination system for providing a fixed current through one or more light sources, compensating for varying input voltages. In its simplest form, the apparatus comprises one or more light sources for radiating light signals, each light source having a corresponding light source current, a power supply, and a current regulation circuit electrically coupled to the one or more light sources, wherein each light source current is maintained at a predetermined level based upon the voltage drop across the current regulation circuit, regardless of wide fluctuations in input voltage.
Specifically, the current regulation circuit of the present invention comprises one or more light emitting diodes, each light source having a corresponding light source current, a transistor, a collector of which is electrically coupled to the one or more light sources, a zener diode electrically coupled to a base of the transistor, an emitter resistor having a first terminal electrically coupled to an emitter of the transistor and a second terminal electrically coupled to ground, the emitter resistor in parallel connection with the zener diode, and a power supply, wherein the current through each light source is maintained at a constant predetermined level based upon the summation of voltage drops across the zener diode, the transistor and the emitter resistor.
The current regulation circuit also includes a bias resister having a first terminal electrically coupled to the power supply and a second terminal electrically coupled to the zener diode and the base of the transistor, the bias resister electrically coupled and in parallel with the light sources. The transistor may be either and NPN-type or a PNP-type transistor. In the case of a PNP-type transistor, the power input and return connection orientation are opposite from the power input and return connection for an NPN-type transistor.
It is an important object of the present invention to provide a current regulation circuit for regulating the current through one or more light sources despite fluctuations in input voltage.
It is another object of the present invention to provide a simple and cost-effective method and apparatus for providing sufficient light in an aircraft lighting system.
It is another object of the present invention to provide a current regulation circuit for regulating the current through one or more light sources in an aircraft emergency evacuation lighting system and maintaining sufficient current through each light source through varying input voltages.
It is another object of the present invention to provide the current regulation circuit in various other aircraft lighting systems including aircraft isle way lighting, instrument panel lighting and rescue lighting.
Still another object of the present invention is to provide a means for providing sufficient lighting to an aircraft evacuation lighting system or similar aircraft-related lighting system which eliminates the inadvertent installation of light modules with incorrect voltage.
It is yet another object of the present invention to provide a single item that provides for sufficient light in an aircraft lighting system thereby reducing the number of parts needed in inventory.
In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.